Thermal erosion of WC-based cemented carbide nozzles by coal water slurry

The nozzle is the most critical part in coal water slurry (CWS) burning system. In this paper, three kinds of WC-based cemented carbides, WC/Co (CCN-1), WC/TiC/Co (CCN-2) and WC/TiC/TaC/Co (CCN-3), which are commonly used in the cutting tools, were produced to be used as CWS nozzle materials. The wear behaviors and failure mechanisms of these nozzles has been studied. Results showed that the hardness and fracture toughness of the nozzle materials plays an important role with respect to the thermal erosive wear resistance of CWS nozzles. The CCN-3 nozzles being with high hardness exhibited lower wear rates, while the CCN-1 nozzles with low hardness showed higher wear rates under the same test conditions. Analysis of eroded bore surface of the nozzles demonstrated that the failure mechanisms of nozzles varied from entry to exit. The failure mechanisms of the nozzle entry zone were mainly brittle fracture with grain pullout, the center zone showed polishing action, while the exit zone of CCN-3 nozzles showed server thermal shock damage such as cracking and collapsing, and the exit surface of CCN-1, CCN-2 exhibited polishing action and grain pullout. Increasing the number of atomizing bores and decreasing inlet angle of nozzle can decrease the nozzle wear.